This invention relates to maleic anhydride copolymer compositions having improved thermally induced reversible cross-linking characteristics. More particularly the invention relates to copolymer compositions containing certain hydroxyl containing derivatives of 4,4'-isopropylidene diphenol (bisphenol A) as cross-linking agents.
The properties of many plastics are generally improved by cross-linking. Cross-linking may be readily accomplished by incorporating in a resin or polymer, a functional group such as hydroxyl, carboxyl, anhydride and the like which can be reacted to cross-link with a variety of di- or polyfunctional materials. However, such thermosetting products generally cannot be remelted and recast or reshaped into a hard cured article or product.
More recently it has been found that with polymers containing an anhydride group the cross-linking is thermally reversible. Such reversible cross-linking with styrene-maleic anhydride copolymers and the like is described in application Ser. No. 618,998 (now U.S. Pat. No. 3,678,016) filed Feb. 27, l967 by R. L. Zimmerman et al. as a continuation-in-part of application Ser. No. 342,812 filed on Feb. 5, l964 and now abandoned. Additionally, U.S. Pat. No. 3,299,184 discloses reversible cross-linking with certain anhydride containing polymers, although the patent points out maleic anhydride containing polymers are generally undesirable.
The utility of such compositions is dependent on the efficiency with which the cross-link bonds are formed, broken and reformed and particularly the efficiency over repetitive cycles of reversing the cross-links. Desirably this efficiency should be at the highest possible level to ensure reworkability and yet not sacrifice any of the properties of the cured cross-linked composition.